The phrase "to get your balls out" means to pluck up the courage to do something. This can be anything, from riding a ferris wheel, to jumping off a tall building.
It is based on the theory every one has the courage or "balls" to do something, it is just a case of "getting them out"

1) guy: You reckon i should go sky diving
other guy: Yeah, Get your balls out and do it!

2) guy: God, that girl is fit, reckon i should get my balls out and ask her on a date?